46 Vniversitij of California Publications in Zoology [Vol. k; 



parabasal bodies, and axostyle of the two cells in one more or le.ss 

 continuous system. 



Binary fission occurs abundantly and normally, with delayed 

 plasmotomy. Normal mitosis occurs with intranuclear spindle, and 

 four chromosomes in two groups. Precocious splitting of chromosomes 

 in the prophase is followed by their fusion into a split skein from 

 which the four chromosomes emerge on the equatorial plate. The 

 blepharoplast and axostyle lead in mitosis. 



Multiple fi.ssion is of three types: (1) Free individuals form a 

 plasmodium-like somatella of eight fully equipped zooids, in the for- 

 mation of which the duplication of organelles keeps pace with nuclear 

 multiplication. (2) Free individuals form eight zooids but nuclear 

 multiplication precedes the division of the organelles. Encystment 

 may follow. (3) Encysted single individuals form 8-zooid, 16-nucleate 

 plasmodial masses with chromatic disintegration of organelles, the 

 axostyles persisting longest. The small free zooids are not to be eon- 

 fused with Hexamitus muris Grassi, which is a distinct species. We 

 find no evidence of an "Octomitus" stage of Giardia. 



There is tentative evidence of the fusion of two free individuals 

 and also of copiilation cysts which may be derived therefrom with the 

 two gametoeyte individuals back to back and of their maturation by 

 two divisions. Chromcsome reduction has not been detected in these 

 divisions. 



The most striking feature of the development of the free, 16- 

 nucleate. 8-zooid Plasmodium, or somatella, is the preservation in each 

 successive step of the process, of the fully equipped binucleate indi- 

 viduals. The individuality of the potential zooids is morphologically 

 established and maintained, and there is evidence also of their func- 

 tional independence in the independent motor struggles of each which 

 result ultimately in plasmotomy. In the cases of multiple fission in 

 cysts and free individuals in which nuclear multiplication outruns 

 that of the other organell&s, this individuality is more or less disrupted, 

 or even lost. The possibility that some of these at least may represent 

 involution or pathological states on the part of the parasite itself, 

 should be borne in mind in all attempts to unravel the baffling signifi- 

 cance of these protean aspects of this most interesting, suggestive, small, 

 but by no means simple organism. 



Zoological Laboratory, University op California, 

 Berkeley, California. 

 Transmitted August 31, 1915. 



